Electromagnetic bone vibrator



fiepto 13, 1949. VERNIER 2,482,044 r ELECTROMAGNETIC BONE VIBRATOR Filed March 29, 1946 6mm" VERNIER INVENTOR.

xi' -4 I HIS ATTORNEYS Patentecl Sept. 13, 1949 UNITED STATE S NT *oiFrieE ELECTROMAGNETIC SBQNE :VIBRA-TQB George Verriier,'0hicago, Ill., assignor toZenith Rajdio Corporation, a corporationnr Illinois Application? March 29, 1946, Serial"No.:.65i,05,0 7

driving member upon which signal voltages are impressed and a driven member supported from the driving member at an optimum distance therefrom wholly ibyrresilient arms or members, oppositelydisposed-Stresses\on the driving member andtthe driven I-member tend to distort the resilient members. If .this distortion exceeds the limits of elasticity of theresilient members permanent distortion:results, the optimum spacing of the driving and driven members is destroyed, and the performance voi the transducer is impaired.

Therefore, it is a principal object ofthis invention to provide -an improved.lelectroemechanical transducerincorporating means for preventing permanent distortion of the resilient members linking the. driving and .driven members.

Another object-oi this invention is to provide an electro-mechanica1transducer .unit having extended longevity.

its afurther-objectof this invention to provide animprovedabone conduction hearing aid receiver having :asensitivity substantially unaffected byhandlingtoflthelreceiver.

Thefeaturesof the present invention which are believed to beenovel aretset forth with particularity iii-the appended" claims. The present invention'itseif, both ,-as=-to:its organization and manner of operation, together with further objects and advantages thereof may best be understood by referencertoithetfollowing description taken iniconnection with accompanying drawing in which:

Figure 1 is a perspective view, partly broken away, of a device'embodying this" invention;

Figure 2 is anexploded view of the device of Figure 1.

In Figures 1 and Z transducer l includes an electromagnetic structure 2 arranged'to generate a magnetic 'field,'a diaphragm? supported in that magnetic field by attaching means, such as screws '4, and separated from electromagnetic structure '2 by diaphragm spacers 5. Winding 6 is arrangednvhen excitedby'signal currents, to vibrate diaphragm 3. "Framel' is supported from electromagnetic structure -2 and is separated therefrom by diaphragm. 3, diaphragm spacers 5, and frame spacerskii ataltdistance such. that it serves as a. stop tto preventthe separation of diaphragm 113 "from structure L2 from becoming v,

large enough to stress arms LS beyOnd'their elastic limit.

I In .detail, relectromagneti'c structure "2, which may The palled the driving member, includes a ferromagnetic frameworkhaving front and back plates .lfiland IlIla -an'd permanentmagnets II and 1'2 supported -.-ther.ebtween .and arranged to have .like poles .in con'tact with opposite ends "of front,p1ate.-'|Ifl. Inadliitionfltheframework incli1des-core J3 supported ,on'the backplate We .magnets ill and 12 through core 13, and flux .exists .acros'sv gap T4. 'Windingffi on core ['3 is arranged .to produce ,a varying *magnetic field when signal voltages are -impressed thereon through? .lea'ds "i5. Threaded openings 1 6 and IT .are providelil'in'firont plate l flito receivescrews 4.

The varying magnetic fluxmroducedbysignal voltages, impressed to on .Wiridinglfilis superimposed on the constant..magnet ic fluxiflowing from permanentmagne'ts l1 ,and, IZ'throughffront or top plate SIB, gap' .14, core 13 and back plate Ina backtothe. respective magnet.

Armature. 2 l, of.ldiaphragm.'3,..being ferromagnetic .and'. being vsupported. in. themagnetic flux path, over gap [4 .between 'top,.plate 10 and core I 3 by symmetrically. id sposednsp in arms l9, assumes iaistat'ic position near core ['3 .whenno signal voltage 'is;impresse'd. on winding 6 and vibrates about 5 that position, .yvithout touching core JliS, when as, signal yoltagejis. impressed on winding'fi. s

Screws '4 pass'throug'h,openingslwuand IS in spring .ar ms,9 toiseeureithose arms.9..0n electromagneticstructu'rel.

.The structure thus iarfdescribed is I identical with that shownland ,described U. ,S. 1 Patent No. "2,459,325, vtit-led iiBone ,,conduction unit, issued..January18,;l949,to,Hugh S.,.-K.nowles and assigned to the same ass'ignee as the present application, In, that structuretoppositely disposed stresses eon arn a'ture ,21l and ielectromagnetic structure 22,- respec.ti zly,v.mayi Itend to separate thetwo excessively iExcessive separation causes springlamsli tgto 'be distorted beyond their elaslim'it, and ther static ,separation of armature I2 I. from core; l'3 isincreased.

Thecspacingsoft-armature 2|}.from core 13 .is impart determinednwhemspringlarmsie are not permanently .distor ted,.;by.. the thickness of dia- .phragm,spacers;5.. The thickness not these:v spacers ischos'ennso that armature 2 Lu'ust failsitostrike sore i3, wherithaarnplitudeotyibration of armature 2| is a maximum. The spacing must not be greater than that necessary to assure such clearance because, for maximum sensitivity, the reluctance of the magnetic circuit including armature 2| should be a minimum. A minimum length of air gap between armature 2| and electromagnetic structure 2 assures minimum reluctance in the magnetic circuit. For a given magnetomotive force the density'of the'fiux produced is then'a maximum and the sensitivity of the transducer is also a maximum.

Cross-arm or stop 22 of frame I is provided to prevent the separation of armature 2| and core |3 from becoming suflicient to distort spring arms 9 permanently. Yoke 23 of framelisintegral with cross arm 22 and includes openings 24 through which screws or other attaching means t pass to secure frame 1 to electromagnetic structure 2.

When transducer is assembled frame I is separated from electromagnetic structure 2 by frame spacers 8, diaphragm 3 and diaphragm spacers 5. Therefore, cross-arm or stop 22 passes over armature 2 l at a fixed distance'from electromagnetic structure 2. The separation of armature 2i from electromagnetic structure 2 cannot exceed this distance. The thickness of frame spacers 8 is chosen so that armature 2| does not strike frame 1 when the amplitude of vibration of armature 2| is a maximum. The thickness is sufiiciently small, however, so thatarmature 2| will strike cross-arm 22 before spring arms 9 are distorted beyond their elasticllimit.

Bracket 25 of frame I is integral with yoke 23 and contains pins 26 to which headband 21a. is removably attached to provide means for supporting transducer upon the human head.

A contact member 21 is coupled to armature 2| by means of screws or fasteners 28 passing through studs 29 into threaded openings 30 in armature 2|. When transducer is assembled studs 29 with armature 2| form a channel 3| through which cross-arm or stop 22 passes, free from contact with contact member 21, studs 29 or armature 2 I. Therefore, contact member 21 is free to respond'to the vibrations or armature 2|.

The outer surface'32 of contact member 21 is so shaped that'transducer fits thejskull structure closely and comfortably when transducer I is worn upon the head, to'assure efficient transmission of vibratory energy from transducer to the skull structure. Openings 33 in contact member 21 permit passage of screws 34 -to attach case 35 which surrounds and protects the internal elements of transducer l.

In applications involving the placement of transducer upon the head in contact with the skull structure near the auditory canalit is customary to grasp case 35 in one hand and headband 21a in the other, spreading headband 21a so that it slips over and springs back upon the head. I

as long as transducer is held so that during this operation the side of transducer formed by contact member 21 faces inward towards the head of the wearer the stress appearing in diaphragm 3 tends to force armature 2| towards electromagnetic structure 2 and transducer is not damaged. However, transducer 1 often becomes twisted by catching in the, hair or clothing of the wearer so that the stresses appearing in diaphragm 3 tend to separate armature 2| from electromagnetic structure 2. Also, in removing the transducer from the pocket and in many other normal phases of handling the transducer, stresses occur which tend to separate armature 2| of diaphragm 3 from electromagnetic structure 2 to an extent which would permanently distort spring arms 9 and would damage the transducer were it not for the existence of cross arm or stop 22 which limits that separation and preserves the sensitivity of the transducer.

In actual tests on a transducer embodying a stop like that of this invention, negligible loss of sensitivity was detected after large distorting forces had been applied. These distorting forces were of the type which would be produced by mishandling of the unit. In a corresponding transducer lacking a stop like that of this invention a loss of sensitivity of approximately 6 decibels occurred as a result of an equal amount of mishandling.

While a particular embodiment of the present invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from this invention in its broader aspects, and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of this invention.

I claim: V

1. In combination, an electromagnetic structure arranged to generate amagnetic field, a diaphragm disposed in said magnetic field and arranged to vibrate in response to variations in the strength of said field, a contact member linked mechanically to said diaphragm'and caused to vibrate thereby, and a cross arm supported from said electromagnetic structure, disposed between said contact member and said diaphragm, and separated from said diaphragm by a distance such that the'maximum possible separation of said diaphragm from'said electromagnetic structure due to oppositely disposed forces on said contact member and said electromagnetic structure is less than that required to produce permanent distortion of said diaphragm.

2. An electro-mechanical transducer including an electromagnetic structure arranged to generate a magnetic field, a diaphragm arranged to vibrate in said magnetic field in response to variations in the strength of said field, a contact member attache'd'to said diaphragm and vibrated thereby, and a frame attached to said electromagnetic structure, said diaphragm being subjected to mechanical stress by simultaneous handling of said contact member and said frame, said stress tending permanently to distort said diaphragm, said frame being provided with a stop member disposed between said diaphragm and said contact member in the region; of maximum displacement of said diaphragm and separated from saidvdiaphragm by a distance such that the maximum possible displacement of said diaphragm from said electromagnetic structure is so small that damaging distortion of said diaphragm cannot occur.

3 An electro-mechanical transducer including an electromagnetic structure arranged to generate a magnetic field, a diaphragm having an armature portion and a spring arm portion integral therewith, said spring arm portion being secured to said electromagnetic structure and supporting said armature in the, magnetic field of said electromagnetic structure, said armature being free to respond to variationsji'n said field, a contact member attached to'said' armature portiOn of said diaphragm and caused to vibrate thereby, and a frame supported on said electromagnetic structure including a cross arm, said cross arm passing between and being free from contact with said diaphragm and said contact member, said cross arm being separated from said diaphragm by such a distance that oppositely disposed stresses on said contact member and said electromagnetic structure can separate said diaphragm from said electromagnetic structure a distance less than that necessary to produce permanent distortion of said spring arm portion of said diaphragm.

4. A hearing aid bone conduction electro-mechanical transducer including an electromagnetic structure arranged to generate a magnetic field, a diaphragm supported from said electromagnetic structure in the magnetic field thereof, said diaphragm being arranged to vibrate in response to variations in said field, diaphragm spacers separating said diaphragm from said electromagnetic structure to allow free vibration of said diaphragm, a frame supported from said electromagnetic structure including a cross arm arranged to pass over said diaphragm on the side of said diaphragm opposite said electromagnetic structure and separated from said diaphragm in the static position of said diaphragm by a distance such that the maximum possible separation of said diaphragm from said electromagnetic structure is less than that necessary to produce permanent distortion of said diaphragm.

5. A hearing aid bone conduction receiver including an electromagnetic structure arranged to generate a magnetic field, a diaphragm supported from said electromagnetic structure in a magnetic field thereof, said diaphragm being responsive to variations in the strength of said field, diaphragm spacers separating said diaphragm from said electromagnetic structure to allow free vibration of said diaphragm, a contact member attached to said diaphragm and caused to vibrate thereby, said contact member being adapted to be placed in contact with the skull structure near the auditory canal, a framework supported from said electromagnetic structure including a stop member arranged to pass between and to be normally free from contact with said diaphragm and said contact member, said cross arm being separated from said diaphragm in the static position of said diaphragm by a distance such that the maximum displacement of said diaphragm from said electromagnetic structure due to oppositely disposed forces on said contact member and said electromagnetic structure is insuificient to produce damaging distortion of said diaphragm.

GEORGE VERNIER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,446,911 Lescarboura Feb. 27, 1923 1,871,739 Ringel Aug. 16, 1932 1,986,955 Bedell Jan. 8, 1935 2,077,425 Lieber Apr. 20, 1937 2,381,673 Lehde Aug. 7, 1945 

